If a loading resistor is needed I'd put it across L5 as the right value may vary depending on the band. Also the 6CL6 might benefit from the added loading.

A general comment. Transmitter layout is one of those simple things.Signals should flow in a linear fashion from low level end to the power endin a direct way. Shielding is used to keep the ins and outs apart. Also subtle things like socket and coil location and orienttion can result in shortest path and most direct routing without crossings. From all appearances the 6dq5 pin one is near the rear (the right of the picture) yet the 6CL6 is to the left. It would seem rotating the tube 90 degrees makes the layout smoother especially if L5 and its shield is situated between them. Looking at the article pictures (magnified) tends to make that a little clearer, but the article gives little direction.

I thought about that, but then thought it wasn't such a good spot. That tuned circuit:

1.) has a 300 pF cap to ground, which means any resistor there will not load the circuit at all on low frequencies

2.) depends on the high impedance of that parallel circuit to invert phase for neutralization

I am a little nervous about VLF stuff in that circuit with all the extra large chokes and a fairly large neut cap. I'd feel a lot better for now de-Q'ing the 1 mH on the grid so it is meaningless.

With a narrow band neutralization system like that, he is best to keep the loading at the grid. If he has a gain flatness issue, there are many ways to handle that. I'd get it stable with minimal effect on other things for now.

The choke is already low Q (Likely under 50) but a 10K across it would be safe.

The 300P to ground is problematic as on 80 its likely too small and on 15 its maybe a bit large.

The parallel tuned circuit can be fairly high and still loaded (typical in some of mine were around 33K). It helps the 6CL6 as sometimes that critter needs a bit of neutralization, an example of that is the HW101. The Tempo-One also loaded the pate of the 12BY7 driver.

The additional problem is the plate of the mixer, grid of the driver and the plate of the driver are all gang tuned.

I haven't seen enough pictures but subtle layout issue can make the whole ampan oscillator. I've seen over the years at least two copies of that TX. one was a clone of the article and worked with only added bypass caps the other was "laid out better" and took work to tame. It needed more screening and any changes in layout are suspect. In both cases the number and placement of bypass caps were wanting and many needed were not shown in the schematic.

There was a design variant of that as a transceiver for 40M in the Mobile Manualand Handbooks.

There was an article in QST years ago entitled, if I remember correctly, 'Just like QST except....' and it went into problems people have by substituting or changing parts.

KW Electronics in the UK produced a copy of the Swan 350, but so it wasn't so obviously a copy, turned it through 90 degrees - producing a form factor more like Drake. The transceiver wasn't brilliant in performance and had a reputation for being a bit unstable. It drifted just like the Swan, too!

Copious thanks again for all the help! I’m totally amazed by how much “tribal knowledge” that is required to bring these ARRL projects to fruition. (I guess the information is there if one scours the handbook thoroughly enough and reads between the lines?)

Today, I paralleled the 1 mH choke with a 2.2K 2 Watt resistor. I do not see any more self-oscillations.I could not locate a 0.5 uFD capacitor in my junk box, so I simply tried the addition of the resistor.I will continue looking for an appropriate capacitor.

My front panel meter says that the 6DQ5 is drawing 30mA as recommended in the calibration instructions provided in the Handbook article. I measure no grid current being drawn.

Here are some images .. Please let me know if anything looks grossly out of order.

There aren't many people that are familiar with this technology any longer.

Anyway, this allows me to go on to the nest steps of getting on the air with this gear!

Thanks again,

KC9KEP

I'm glad it worked out.

If the rig has any gain-flatness issues, we can work them out while improving IMD at the same time.

When I was 11 or 12, I wanted desperately to be a Ham. We were very poor, with dirt floors in some rooms, so I had no choice but to build things. Since I couldn't buy parts, I had to get them from the dump and from people's throw away stuff.

Since I wanted to get on the air, and I could not copy any article, I had to read and experiment and learn how this old stuff worked. It kept me alive and out of trouble, most of my friends were dead by the time I was in my 20's. This is why I really love seeing someone else build stuff from that era. I'm just so envious of you, Tom, and the neat work you do.

If you lived near me, I'd be a real pest. We'd start a new company, like Collins.

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